In processes for the production of semiconductor devices, for example, IC or LSI, fine fabrication is conducted by means of lithography using a photoresist composition. In recent years, as the degree of integration in integrated circuits increases, it has been requested to form an ultra fine pattern in the submicron region or the quarter micron region. With such a trend, an exposure wavelength tends to become shorter, for example, from g-line to i-line and further to a KrF excimer laser beam. Moreover, the development of lithography using an electron beam, an X ray or an EUV beam also proceeds at present in addition to the use of an excimer laser beam.
However, as the degree of integration in integrated circuits increases as described above, resolution limit of a conventional monolayer resist becomes clear and a method of forming fine patterns having a large thickness by using a two-layer resist in place of the monolayer resist is proposed. Specifically, a thick layer of an organic polymer is formed as a lower layer, a thin resist material layer is formed as an upper layer on the lower layer, and then a high energy beam is irradiated to the upper resist material layer, followed by development. Thereafter, the lower organic polymer layer is subjected to oxygen plasma etching using the pattern thus-formed as a mask to prepare a pattern having a high aspect ratio. In such a case, since the upper resist layer must have high resistance to the oxygen plasma, a silicon-containing polymer is ordinarily used in the upper resist layer. Particularly, in order to increase the silicon content, many attempts to use an acid-decomposable group-containing polysiloxane or polysilsesquioxane that has silicon atoms in the main chain of the polymer have been made.
Particularly, with respect to lithography of next generation or after the next generation using an electron beam or an EUV beam, it has been strongly desired to increase sensitivity of resist for the purposes of reducing a processing time of wafer and decreasing damage to an apparatus. However, when high sensitivity is tried to pursue with respect to a positive resist, not only decrease in resolution but also deterioration of line edge roughness occur. Thus, development of resist that satisfies these characteristics at the same time has been strongly required. The term “line edge roughness” as used herein means a phenomenon wherein an edge between a line pattern of resist and a surface of substrate irregularly fluctuates in the direction vertical to the line due to the characteristics of resist, and the edge looks uneven when the pattern is observed from just above. Since the unevenness is transferred to the substrate in an etching step using the resist as a mask, the unevenness causes deterioration in electric properties thereby resulting in the yield reduction. Particularly, in an ultra fine range of 0.25 μm or less, the line edge roughness is a very important subject to be improved. A trade off relation between high sensitivity and high resolution, good pattern profile and good line edge roughness exists in the resist composition, and it is very important that these characteristics are satisfied at the same time.
Many attempts to use an acid-decomposable group-containing polysiloxane or polysilsesquioxane have been hitherto made as described, for example, in Patent Documents 1 to 8. Further, as an example of application of a silicon-containing two-layer resist to the electron beam lithography, a positive resist using a polysilphenylenesiloxane polymer described in Non-Patent Document 1.
However, in the present circumstances, any of these techniques cannot fulfill requirements for high sensitivity, high resolution and good line edge roughness at the same time in the ultra fine region.
Patent Document 1: JP-A-6-184311 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)
Patent Document 2: JP-A-8-160620
Patent Document 3: JP-A-9-274319
Patent Document 4: JP-A-2001-147538
Patent Document 5: JP-A-2002-6494
Patent Document 6: JP-A-2001-330957
Patent Document 7: JP-A-2000-219743
Patent Document 8: JP-A-2001-109150
Non-Patent Document 1: Journal of Photopolymer Science and Technology, Vol. 9, page 697 (1996)